ARTICLE BY ANDY SAUNDERS
The body reacts to noise as a danger signal. Our nervous systems
haven't had time to evolve from the time when the loudest noise you'd
hear would be a mammoth charging at you. When we're exposed to loud
noise, blood pressure rises, heart rate and breathing speed up,
muscles tense, perspiration increases and hormones are released into
the bloodstream. It's in your best interest to keep the noise in your
life to a minimum.
Everyone has felt ringing in their ears after a loud concert or a
party; continued abuse of your ears makes that ringing (called
tinnitus) permanent. Although loud noise can damage your ears (usually
irreparably), it affects the heart most. Blood vessels constrict,
pressure rises and cholesterol and triglycerides also rise. The
increased hormonal activity steps up the secretion of acid in the
stomach, possibly causing ulcers.
Loud sounds also affect the reproductive system in a manner similar to
alcohol: increasing sexual drive while decreasing potency. In
addition, loud sounds affect the level of white blood cells and gamma
globulin in the bloodstream, lowering the efficiency of the immune
system.
Sound is measured two ways: by level and by the frequencies that make
up that level. The adolescent human ear can hear sound waves at levels
between a low 20 cycles per second, or 20 hertz (Hz), and a high of
20,000 cycles per second, or 20 kilohertz (kHz). Low frequencies are a
dull rumble, high frequencies a shrill whine. As we get older,
frequency response drops. A middle-aged person may not hear beyond
10,000 Hz (10 kHz). The human ear is most sensitive to sounds in the 1
to 4 kHz range, the usual frequencies of human speech, and damage
occurs first in these areas.
Hearing loss is a gradual process, unnoticed by the loser. Noise
doesn't have to hurt your ears to hurt your hearing: the Occupational
Safety and Health Administration advises that habitual exposures to 85
dB for more than eight hours cause hearing loss. If you are regularly
exposed to noise at the 95-dB level (10 times as loud), one hour is
about the limit. Above 105 dB, your hearing can be damaged by repeated
15-minute journeys.
Motorcyclists risk hearing loss. Noise is the constant companion of a
motorcyclist, no matter how quiet the bike. Pushing any projectile
through the air at speed creates turbulence and noise, whether that
projectile is a rifle bullet, an airplane or a human head. Riding
with a bucket on your head creates more turbulence at the mouth of
the bucket, and more noise. Some (though very few) full-face helmets
can be noisier than no helmet at all.
Even the best helmets can't close out all the wind noise, so if you
ride long distances frequently, you need to wear ear protection. The
most convenient, the foam earplugs of the E.A.R. type, cut
sound-pressure levels by 30 dB or so when properly inserted, and
nearly every California motojournalist uses them. Unfortunately, they
are all breaking the law.
California's vehicle code states: "No person operating a motor vehicle
or bicycle shall wear any headset covering, or earplugs, in both ears.
The prohibition does not apply to any person wearing hearing
protectors in the form of custom earplugs or molds that are designed
in a manner so as to not inhibit the wearer's ability to hear a siren
or horn from an emergency vehicle or a horn from another motor
vehicle."
Of course, you can buy custom earplugs, but they are uncomfortable
inside a well-fitting full-face helmet and expensive at around $100 a
set.
Avoiding damage to your brain is more important than avoiding damage
to your hearing, but by selecting the right helmet, you can do both.
The results are interesting. The quietest helmet at 60 mph is much
quieter than the loudest at 30, and the loudest helmet has the
potential to damage hearing after quite a short exposure. At 30 mph,
the padding of the open-face Bell was springy enough to effectively
insulate the ears. At 60, the padding had deflected enough to make it
one of the noisiest helmets.
Due to the dfflerence between the human ear and electronic
microphones, we expected the noise-test results to disagree with
tester's subjective evaluation but we were pleasantly surprised. With
a couple of notable exceptions, what we heard is what the machine got.
The exceptions: The Kiwi K22 seems quieter than it is, the Sure
louder. The Kiwi seems quieter because all its noise is low in
frequency, and even at 60 mph the frequency level doesn't intrude much
into the speech band of 1 to 4 kHz. The Sure has exactly the same dB
level at 60 mph, and in fact is quieter at 30 than the Kiwi, but it
seems louder and more unpleasant because a significant component of
its noise occurs in the speech band.
We expected that our favorite, high-priced helmets would do well on
this test, and we were right. As a nule, the higher the price, the
better padding and noise protection. The exceptions were AGV's Phantom
and Thema, where price seems directly proportional to noise level.
(But these helmets are also light, with large eye ports.)
Shoei's X8, touted as the quietest, most aerodynamic helmet on the
market, is quiet because it has more sound-deadening padding in the
comfort liner and is sized to fit very tightly. Our tester, who is on
the borderline between large and extra large in Shoei sizes, found he
was more comfortable in a large-model RF200 than an extra-large X8;
the RF200 was quieter too.
Would riding without a helmet do more damage to your hearing? Yes.
Research shows that almost any open or full-face helmet attenuate
enough sound to afford some hearing protection. Shorty helmets are a
real hearing risk, and motorcycle policemen may suffer significant
hearing loss after years of wearing one (which should give cops who
want better helmets a strong case).
A helmet that has less sound insulation will not necessarily allow
you to hear more at highway speeds. For a specific sound to be
audible, the signal-to-noise ratio would theoretically have to be
greater than 1-to-1. In other words, if you are experiencing a
110-dB roar in your helmet, any siren or horn will have to be louder
than 110 dB for you to hear it (in practice, sirens operate at high
frequencies, so you may hear one even when the signal-to-noise ratio
is less than 1-to-1). Earplugs effectively dampen wind noise, yet
allow shrill sirens to be heard clearly. However, if you drive in very
slow traffic most of the time, where you need to notice external
environmental sounds, a quiet helmet with thick padding may mask some
of these essential sounds.
These tests were perforrned without engine or external traffic noise,
so they represent the minimum noise present at those speeds. Engine
noise and external traffic noise add to the racket inside your helmet,
though you'll notice it more at 30 mph than at 60 mph. Helmets like
the Sure S8-N, AGV Sukhoi, Bieffe B3R, CTS, Fulmer, Hondaline, MDS,
Nolan N35 and Jeb's all sounded louder than their rankings would
suggest. None of these are fiberglass lids, suggesting that the type
of material used in construction may play a part or that the cost of
materials has an effect. Certainly, the fit between face shield and
shell was important. The wind whistled through the gaps in the Sure's
shield, adding to the cacophony.
The plastic helmets were also at a relative disadvantage due to their
single shell size. Helmets sized large or extra large were used
exclusively for this test, and the polycarbonate lids have only one
size shell for all head sizes. Thus, extra-small wearers get much more
EPS and comfort linerŅ and more sound attenuation.
How much are you at risk? If you wear a well-fitting, quiet helmet on
short journeys to work every day, you'll probably never need ear
protection. But motorcyclists who ride often or far; couriers,
policemen, motojournalists and high-mileage touring riders do need
protection.
You may find that a helmet-closure device, like Noj's chin shield or
Lockhart's Apple Warmer, will cut down the level of sound reaching
your ears, although the face shield will fog up more easily and you'll
experience more heat in warm weather.
A future generation of helmets is likely to offer active
noise-reduction (ANR) technology, currently in use in airplane
headsets. ANR works by generating mirror-image sound waves, waves of
opposite phase, for every component of the environment's noise. The
two sound waves cancel each other out. Since even the best current ANR
system takes a few seconds to precisely analyze and duplicate the
sound-wave components of noise, ANR will work best on touring
machines, where noise remains constant. Sport-bike owners, don't
throw away your earplugs.